1. Field of the Invention
The present invention relates to a method and an apparatus for processing digital image data to be used in an image forming apparatus, such as an optical printer (e.g., a laser printer), a digital copying machine, and a plain-paper facsimile, etc., and more particularly to a method and an apparatus that can improve a quality of resultant images produced by such an apparatus.
2. Discussion of the Background
Japanese Patent Laid-Open Publication No. 5-207282 discloses a method for correcting jags on an outline of bit-mapped image data so as to improve the quality of resultant images. By using such a method, the amount of data stored in a memory to perform the above-mentioned correction on the bit-mapped image can be reduced. Further, in this method, it is rapidly determined which dots in the image data are to be corrected, and which type of correction is required. The determination is also made in an extremely short time by simple logical operations using a microprocessor.
According to the above-mentioned method, characteristics of a line shape of a boundary between a black-dot region and a white-dot region of image data in a bit-map formation are recognized. The recognized characteristics for each dot of the image data are then converted into multi-bit code information. Then, at least a part of the code information is used to determine whether or not the relevant dot is one to be corrected. When the dot is determined as requiring correction, the correction is performed on the dot based on the above-described code information.
An image data processing apparatus, which performs the above-described image data processing method, includes a window and a pattern recognizing means. The window extracts data of dots in a predetermined region of the bit-mapped image data, and the region includes a relevant dot in the center thereof. The pattern recognizing means recognizes the line shape of the boundary between the black-dot region and the white-dot region of the image data extracted by the window so as to generate the multi-bit code information showing the recognized line shapes of the dots. The apparatus also includes a determining means and a correction data memory. The determining means determines whether or not dots are to be corrected using at least a part of the code information. The correction data memory reads and outputs previously stored correction data for the dots to be corrected using the code information generated by the pattern recognizing means as a corresponding address.
Further, in the above-described method, it is not necessary to provide and store as templates all characteristic patterns which are corrected. The determination as to which dots are to be corrected and which correction data is required for the dots can simply be made in a short time.
In another method disclosed in Japanese Patent Laid-Open Publication No. 7-87321, a magnification of image data and a density conversion of the image data to increase a resolution are performed at the same time when a jag-correction is performed. This is accomplished by adding the information of the image data in both a main scanning and a sub-scanning directions to the above-mentioned code information.
However, the above background art method does not have a function to reduce image data. According to a method in which a reduction of image data is described, the reduction of the image data is performed by controlling whether or not the image data previously stored in a page memory is read out. In this method, the reduction of the image data is performed by a simple deletion of an original image data or by discontinuously performing a plurality of readouts of the original image data. In the method in which the simple deletion of the original image is made, degradation in the quality of a resultant image might occur. In the method in which a plurality of readouts of the original image is discontinuously performed, although the degradation in the image quality may hardly occur, little effect of the jag-correction is obtained.
In addition, when a reduction or an enlargement of image data in size is performed, complicated calculations are required for adjusting a position of the resultant reduced or enlarged image in a printing sheet.